When a resistor element is formed in a semiconductor device such as an integrated circuit and the like, frequently a resistor thin film is formed between silicon thin films. In this arrangement, the silicon thin film protects the resistor thin film.
FIG. 4 shows an example of this arrangement in which a resistor element having the above described structure was used in an integrated circuit.
In FIG. 4, numeral 11 denotes an insulating layer which has been formed on a semiconductor substrate (not shown in the figure). Numeral 12 denotes a silicon layer formed in thin film-like form, numeral 13 denotes a resistor layer formed in thin film-like form on this silicon layer 12, and numeral 14 denotes a silicon layer formed on this resistor layer 13. Numeral 16 is a protective insulating layer for which silicon oxide is ordinarily used. Numeral 18 denotes a metal layer which is connected to the resistor layer 13 via a contact hole 17.
In the above described conventional resistor element, the film thickness of the silicon layers 12 and 14 has been restricted for the following reasons. When the film is too thin, the silicon layers 12 and 14 can not sufficiently protect the resistor layer 13. On the other hand, when the film thickness is too great, a eutectic reaction is generated between the silicon layer 14 and the metal layer 18, and the resistance value changes. Due to this fact, the film of the silicon layer 14 is restricted to have a thickness such as 3 nanometers, and the control of the thickness of the silicon layer 14 is difficult.
In addition, in the above-described conventional resistance element, since the surface of the silicon layer 14 is exposed to the atmosphere during production procedure, the silicon layer 14 is oxidized to form silicon oxide. As a result, when a contact hole is formed by etching the protective insulating layer 16, the silicon layer 14, which is intended to function primarily as a stopper for etching, is also simultaneously etched. Consequently, even the resistor layer is subjected to the etching action, and such problems as bad contact to the resistor and change of the resistance value arise.